A bluegrass mandolin, typically F-style, is one that is loud and bright-sounding, set up to play hard because they really thrash em! What it usually doesn't have is a lot of sustain, so it's not ideal for Celtic tunes where you want a sweet, ringing sound that lasts. (In bluegrass style if you want a sustain-note you play a tremolo--picking the same note back-and-forth very fast--so the sustain is not important, you don't wait to hear it.)

My current mando which I've had for 10 years is one of the many A-50 style copies out there, a cheapo (famous name, though: Bentley!) which I paid $85 U.S. for at a festival. (And yes it does have f-holes. The much-admired early Gibson A series, Model A through A-5, have round soundholes).

A few things to look for in evaluating a mandolin: is the top solid and carved (it is if it has raised relief lines, like ridges on it) or is it plywood? Solid top is better, but plywood can be fine if the price is right.

The holy grail, bluegrass or newgrass is Gibson F-5 from the Lloyd Loar (acoustic engineer) period--till 1923 or so. These go for 30,000 U.S. up. Fortunately the wonderful Gibson A's from the same period are much cheaper--starting at about $800 U.S. now, and I want one. Aside from the usual wear, model (higher the number the more $) and playability, there's a premium value on what they call a "snakehead" style peghead. This is the type that is narrower towards the end--I think it separates the strings better at the pegs which reduces buzzing and that kind of problem.

Remarks I have made about cheap guitars are applicable here as well--a knowledgeable player will be able to pick out the maybe one in 10 or 20 of a bunch of cheap ($200) mandos that's a good one. It's not entirely subjective.

More people should play mandolin, it's a good antidote to too-many-guitars-and-fiddles.

Willie-O